67 L36/68 cast steel crank?

[Tim S.]

It is my understanding that the 1967 L36/68 hydraulic cam,oval port head BB cars originally had a cast steel crankshaft not a forged steel crankshaft such as the 6223 one; and that the harmonic balancer was 7" not 8" in diameter. Can anyone confirm this and also tell me if the correct cast crank casting number is 38014816. Is it also true that any cast 396 or 427 crank will work dementionally.
Thank You

[Joe L.]

Re: 67 L36/68 cast steel crank?

It is my understanding that the 1967 L36/68 hydraulic cam,oval port head BB cars originally had a cast steel crankshaft not a forged steel crankshaft such as the 6223 one; and that the harmonic balancer was 7" not 8" in diameter. Can anyone confirm this and also tell me if the correct cast crank casting number is 38014816. Is it also true that any cast 396 or 427 crank will work dementionally.
Thank You

Tim----

No cast steel or cast iron crankshaft was ever used for a Corvette 427 cid engine. In fact, as far as 427 engines go, a cast iron crank is rare and a forged steel crank common. It's the opposite for 454's----cast cranks are common and forged cranks are rare.

The L-36 and L-68 engines used a 7" balancer.

The "6223" forging number crank is one of those used for 427 Corvette engines. The 3856223 may also have been used, although it was primarily a 396 crank. The 396 and 427 cranks are generally interchangeable but may require re-balancing. Balancing of the reciprocating assembly should always be done before a new crankshaft or other new reciprocating parts are installed, anyway.

3804816 was a crankshaft used for both 396 and 427 engines. However, I don't know if it was ever used for Corvette engines. I do not know what material this crankshaft was manufactured from.

[Tim S.]

Re: 67 L36/68 cast steel crank?

Joe

Thank you for the information, in this case I am glad to be in error. I just torn down a L-68 engine, and it had a 6223 crank and 7" balancer so it is correct for this application. That is a relief.
So the forged steel cranks could have either harmonic balancer i.e., 7" L/36/68 and 8" for the solid lifter square port head cars L/71.L89,L-88 ?

Thanks again
Tim

[Joe L.]

Re: 67 L36/68 cast steel crank?

Joe

Thank you for the information, in this case I am glad to be in error. I just torn down a L-68 engine, and it had a 6223 crank and 7" balancer so it is correct for this application. That is a relief.
So the forged steel cranks could have either harmonic balancer i.e., 7" L/36/68 and 8" for the solid lifter square port head cars L/71.L89,L-88 ?

Thanks again
Tim

Tim----


Yes, that's how it was as far as 427 cid engines in Corvettes were concerned. There were a few different versions of the 8" balancer, though, just slightly different in tuning. For Corvette 454's, all used an 8" balancer, although several differently tuned versions were used.

[Steven S.]

Re: 67 L36/68 cast steel crank?

I was under the impression that the auto cars got cast iron cranks and the stick cars got the forged steel. I suppose then this might have been the case only with passenger car. I had an Impala auto. 335hp 427 that had a cast crank.

Steve

[Joe L.]

Re: 67 L36/68 cast steel crank?

I was under the impression that the auto cars got cast iron cranks and the stick cars got the forged steel. I suppose then this might have been the case only with passenger car. I had an Impala auto. 335hp 427 that had a cast crank.

Steve

Steve-----


Are you sure the 427 Impala had a cast crank? In other words, did you actually have the crank out of the engine and observe the parting line difference? There was no difference with cranks as far as transmission application goes. The 66-69 passenger cars with L-36 427 used the same crank as 66-69 Corvettes with L-36 and L-68. It was GM PART #3882849 and this is a forged steel crank.

[Joe L.]

Re: 67 L36/68 cast steel crank?

I was under the impression that the auto cars got cast iron cranks and the stick cars got the forged steel. I suppose then this might have been the case only with passenger car. I had an Impala auto. 335hp 427 that had a cast crank.

Steve

Steve-----


I did a little more checking. It turns out that 1969 with 335hp 427 used a different crankshaft than 1966-69 L-36. It was GM PART #3937739. I do not know what material this crankshaft was manufactured from.

[Steven S.]

Re: 67 L36/68 cast steel crank?

Hi Joe ,
I can't confirm the GM part number, but the crank out of this engine has cast # 3904815 , which according to Mortec is a 396/402 cast nodular iron crankshaft. As far as the crank being original to the engine I removed it from, I would be genuinely shocked if it were not.

Steve

[Joe L.]

Re: 67 L36/68 cast steel crank?

Hi Joe ,
I can't confirm the GM part number, but the crank out of this engine has cast # 3904815 , which according to Mortec is a 396/402 cast nodular iron crankshaft. As far as the crank being original to the engine I removed it from, I would be genuinely shocked if it were not.

Steve

Steve-----


It's very possible, even likely, that the GM PART #3937739 crankshaft used the 3904815 casting. So, with your information, I now know that the 3937739 was a cast crank.

A curious piece of trivia here is that, in 1969, the 3937739 crankshaft (which I now know was a casting) actually cost MORE than most of the 427 forged cranks and only $4 less than the 1969 L-88 crank. This probably reflected the fact that forged 427 cranks were, at that time, being manufactured in much higher quantities than the cast 427 cranks.

[Steven S.]

Re: 67 L36/68 cast steel crank?

Interesting... kind of makes you wonder why they would have made the switch?

At any rate, hopefully this info will helps someone at some point!

Thanks,
Steve